Magnetic resonance imaging (MRI) is a well established technique that is used, for example, to discriminate between normal and pathological tissue samples. MRI image contrast in this technology depends on differences in parameters such as the proton density, the longitudinal relaxation time T1, and the transverse relaxation time T2 for different media. MRI is also used in contexts where parameters such as the magnitude and phase of the transverse magnetization, the magnitude of the longitudinal magnetization, and the resonance frequency (related to spectroscopy) are related to functions such as molecular displacements (e.g., flow and diffusion).
In magnetic resonance imaging (MRI), specialized radio frequency (RF) pulses are typically used to stimulate susceptible protons so that image information may be collected. Three axes, X, Y, and Z, are employed to acquire sufficient positional information about each proton to construct a three dimensional image. Further, each of the three axes is not uniform but comprises a magnetic gradient, allowing each proton to be measured relative to the axis by its position within the gradient.
Because MRI acquires information about susceptible protons, typically hydrogen protons, water and water containing fluids are a common imaging target. In the realm of medical imaging this allows the imaging of diffusion processes involving a wide variety of physiological solutions including those in blood, cerebrospinal fluid, or other water containing bodily fluids. Because fluids are relatively mobile compared to other bodily tissues, special imaging techniques must often be employed.